The invention generally relates to systems for monitoring error in measuring apparatus. More particularly, the invention relates to weighing apparatus in systems for transferring fluids from individual source containers to a single receiving container. Yet more particularly, the invention relates to weighing apparatus in systems for transferring liquid drugs from individual vials, bottles, or bags to a single solution bottle or bag for administration to a patient.
In hospitals, it is frequently necessary to provide solutions for intravenous administration to a patient which contain a variety of drugs in a single solution container. A common example of such a need arises when a patient is receiving all of his nutritional needs intravenously. In this situation, the patient will typically receive a basic solution containing amino acids, dextrose, and fat emulsions which provide a major portion of the patient's nutritional needs. However, this solution is insufficient to maintain a patient for an extended period of time. Therefore, a typical total parenteral solution includes as many as eight to twelve additional additives. The additives are typically minute quantities of vitamins, minerals, electrolytes, etc. Therefore, when a pharmacist is preparing a solution for total parenteral nutrition, it is necessary for the pharmacist to individually add each of the additional additives to a solution container after the base solutions have been added. This is typically done with individual syringes and requires a relatively long "hands on" time on the part of a pharmacist to accurately add all additives to each of the required additives. Further, manual additive addition requires multiple entries into the patient container and volumetric quality control is difficult to maintain.
An automatic compounding device developed to assist a pharmacist in preparing solutions for total parenteral nutrition is described in U.S. Pat. Nos. 4,467,844 and 4,513,796 which are incorporated herein by reference. This device is used to assist the pharmacist in automatically compounding the base solution of amino acids, dextrose and fat emulsions. This system typically uses three or more peristaltic pumps to individually pump each of the base solutions from three or more separate source containers. Computer software also has been developed and is currently being used to program in the amount of solution required for a series of individual patients. This program is designed to operate the automated compounding equipment described in each of the above patents. This program is more fully described in U.S. patent application No. 665,268 filed Oct. 26, 1984, now U.S. Pat. No. 4,653,010 which is also incorporated herein in by reference.
While the above-described system has provided a tremendous advantage to the pharmacist, it is not useful for adding minute quantities of fluid additives to the receiving container. U.S. Pat. No. 4,789,014 discloses a device which can very accurately dispense very small quantities of fluids into a receiving container. U.S. Pat. No. 4,789,014 is fully incorporated herein.
In the device disclosed in U.S. Pat. No. 4,789,014, disposable transfer sets are removeably installed in the system to provide fluid conduits between various source fluid vials and a receiving container. A load cell is employed to measure quantities of fluids added to the receiving container.
The load cell can measure quantities on the order of a single droplet. As such, the load cell is highly sensitive.
After the installation of a transfer set, it is possible for a load cell of a compounding device such as that disclosed in U.S. Pat. No. 4,789,014 to be affected such that a significant margin of error can be present. However, this margin of error diminishes over time as the load cell stabilizes.
It would be advantageous to prevent operation of a device such as that disclosed in U.S. Pat. No. 4,789,014 until accurate load cell readings can be obtained so as to prevent erroneous measurement of fluids. Erroneous measurement of fluids can lead to the administration of incorrect doses of medication and the like, which may harm a patient.